Conventionally, a brushless motor apparatus is used as the driving source of an on-vehicle EGR (Exhaust Gas Recirculation) valve or an actuator for exhaust emission control such as a VG (Variable Geometric) turbo actuator, for example. The brushless motor apparatus includes, for example, a stator where the number of its slots is “9,” a rotor where the number of its poles is “8,” a magnetic-pole-position detecting magnet where the number of its poles is the same as that of the rotor “8,” and a Hall element detecting the rotational position of the rotor by detecting the magnetism of the magnetic-pole-position detecting magnet.
In recent years, a brushless motor apparatus where the number of poles of the magnetic-pole-position detecting magnet is “16” that is twice as large as that of a conventional detecting magnet has been developed in order to increase the resolution in the detection of the rotational position of the rotor (see Patent Document 1, for example). The brushless motor apparatus can double the accuracy with which a conventional brushless motor apparatus detects the rotational position of the rotor.
Patent Document 1: JP-A-2002-252958
In the brushless motor apparatus disclosed in Patent Document 1 described above, it is required to first detect the phase of the rotor upon actuation of a power source. The phase detection is done by giving current supply patterns sequentially to the stator at a fixed duty cycle to switch excitation patterns in sequence; however, when the rotor rotates by those excitation patterns and stops at stabilization points according to the excitation patterns, mechanical vibration is caused in the time elapsing before the rotor rests at a stabilization point. Since the engine is not yet usually started upon actuation of the power source, the surroundings are very quiet. Therefore, there occurs a problem that the mechanical vibration caused by the rotation of the rotor is transferred to the shaft or other linkage mechanisms to cause the reverberating sounds to grate on the ear.
Further, since the number of poles of the magnetic-pole-position detecting magnet is increased twice as large as that of conventional one, even if, as shown in FIG. 6(a), the state of the output patterns of three Hall ICs (an IC into which Hall elements are built) arranged so as to be opposed to the magnetic-pole-position detecting magnet completes a full circle, the amount of travel of the rotor (the amount of rotation of the rotor) brought by the excitation patterns is half that of the conventional detecting magnet. For this reason, it is required to judge whether the state of the output patterns of the Hall ICs assuming the present position belongs to area A or area B. If the present position thereof is judged to exist in area B in spite of the fact that the position actually exists in area A, there occurs a problem such that the direction where the rotor is to be rotated may be opposite from an intended direction.
The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a brushless motor apparatus where the generation of sound grating on the ear occurring upon actuation of the power source can be reduced, and the rotation of the rotor in the direction opposite from the intended one can be prevented.